The present invention relates to a projection television set including a combination of three cathode ray tubes (CRTs) and projection lens systems for the three primary colors, i.e., red, green and blue.
FIG. 7 shows an example of prior-art projection television set. As illustrated, it comprises a video signal processor SP, three CRTs TR, TG and TB, three projection lens systems LR, LG and LB and a screen SC. The video signal processor produces video signals for red, green and blue components, which are supplied to the three CRTs TR, TG and TB. Images produced on the CRT fluorescent surfaces of the CRTs are passed through and enlarged by the projection lens systems LR, LG and LG, respectively and projected onto a projection television screen SC. A problem associated with the prior art television set is that the fidelity of green color is not satisfactory in certain applications.
FIG. 6 shows an example of the green projection lens system LG and the associated CRT TG. In the figure, reference numeral 1 denotes CRT face glass. Reference numeral 2 denotes a CRT fluorescent surface. Reference numerals 3, 4 and 5 denote a first, second and third projection lens elements. In the projection lens system as illustrated in FIG. 6, light emitted from a green CRT fluorescent surface 2 having a light-emitting spectrum indicated by solid lines 10, 11 and 12 in FIG. 2 passes through the projection lens elements 3, 4 and 5 is and enlarged and projected on the projection television screen SC. The color reproduction of green light as projected on the screen SC is at the chromaticity point 15 in the x, y chromaticity diagram of FIG. 3.
Because the prior-art projection lens system is constructed as described above, the unnecessary light component in the green light-emitting spectrum is also projected. Thus, is not possible to secure the same color reproduction range achieved with a standard television.